Personalized Fluid Assessment

ABSTRACT

A system and method of monitoring the fluid status of a patient. The system may include a patient monitor that receives blood pressure data. A first fluid model receives the blood pressure data, and a personalized fluid model is derived from the application of the blood pressure data to the first fluid model. An estimation of the patient&#39;s fluid status may be derived from the personalized fluid model. The method may include the steps of measuring a first blood pressure value, creating a personalized fluid model, measuring a second blood pressure value, applying the second blood pressure value to the personalized fluid model; and deriving an estimation of the fluid status of the patient.

FIELD OF THE DISCLOSURE

The present disclosure relates to the field of monitoring patientphysiological parameters. More specifically, the present disclosurerelates to the indirect monitoring of patient fluid status.

BACKGROUND

In critical care and other medical care situations, the parameter offluid status is an important parameter to be monitored. The patient'sfluid status generally refers to the volume, or change in volume, ofblood presently in the circulatory system of the patient.

A change in the patient's blood volume due to hypervolemia or excessivefluid, or hypovolemia, or reduced fluid volume, can result in variousautonomic responses by the organ systems of the patient. Asbaroreceptors detect a change in the fluid volume, the organ functionsimilarly changes to accommodate for the addition or loss of fluid.These autonomic responses attempt to maintain appropriate bodilyfunction in response to the change in fluid volume.

Another effect of a change in fluid volume is the impact onpharmacokinetic and pharmacodynamic models used by clinicians indetermining the proper drug dosage, the resulting drug concentration inthe body, and the body's metabolism of the drugs currently in itssystem.

One exemplary situation where the fluid status of the patient is animportant physiological parameter is that of a critical care situation,such as during an invasive surgery. During such surgery, theanesthesiologist must continuously monitor the patient's vital signs todetermine the proper drug concentrations to be delivered to the patient.The vital signs, including the patient's heart rate, temperature, bloodpressure and breath rate, all may be affected by the patient's autonomicresponse to a change in fluid status. These vital signs are allimportant to determine the proper drug concentrations and fluids to bedelivered to the patient. This is conducted in a situation in which thepatient may experience significant changes in fluid status. Sources offluid status change include bleeding, dehydration via tissue exposed toair at the surgical site, urine production, and the administration ofintravenous fluids, including crystalloids or colloids.

Current techniques for monitoring the patient's fluid status are limitedfor being complex, inaccurate, or subjective. Techniques such asmeasuring capillary refill time (or the time that it takes for blood toreturn to nail bed tissue after pressure has been applied) aresubjective and qualitative evaluations of fluid status. Techniques suchas transesophagal echo that utilize ultrasound to monitor fluid movementin the thoracic cavity are invasive, especially in situations when thepatient requires mechanical ventilation. Alternatively, an estimation offluid status may be made by actively charting all of the fluid into andout of the patient. This estimation is labor intensive and is limited inits ability to provide timely fluid status levels.

BRIEF DISCLOSURE

The present disclosure relates to the field of patient fluid statusmonitoring. Embodiments of a system for estimating the fluid status of apatient are described in more detail herein. In an embodiment, a patientmonitor receives patient physiological data. This patient physiologicaldata is transferred into a first fluid model in order to calibrate thefirst fluid model to create a personalized fluid model based on themonitored physiological data. The personalized fluid model may then beused to derive an estimation of the patient's fluid status at a latertime or date.

Embodiments of a method of estimating the fluid status of a patient arealso disclosed herein. Such embodiments may include the step ofobtaining a fluid model. Next, a first blood pressure value is measured.The fluid model and, the first blood pressure value, are used to createa personalized fluid model for the patient. Next, a second bloodpressure value is measured and applied to the personalized fluid model.Finally, a patient fluid status estimated value is calculated from thepersonalized fluid model.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a fluid assessmentsystem;

FIG. 2 is a schematic diagram of an embodiment of a fluid model; and

FIG. 3 is a flow chart depicting the steps in an embodiment of a methodof providing personalized fluid assessment.

DETAILED DISCLOSURE

Systolic pressure variation (SPV) is a physiological phenomenon found inthe continuous arterial blood pressure of a patient receiving positivepressure ventilation (PPV). The PPV causes a cyclical change inintra-thoracic pressure experienced by the patient. The increase inintra-thoracic pressure during inhalation causes a decrease in the leftventricular after load by increasing the pressure gradient between theaorta and the systemic vasculature. These effects attenuate as theintra-thoracic pressure decreases during exhalation. The additionalpressure also decreases the venus return by decreasing the pressuregradient between the vena cava and the right atrium. The overall effectseen in the monitored arterial blood pressure is that an increase in thesystolic, or maximum, blood pressure (Δ up) is found during the periodsof inhalation, while a decrease in the measured systolic pressure (Δdown) is found during exhalation.

The difference between the measured systolic pressure during inhalationversus exhalation is the measured systolic pressure variation (SPV).Clinical tests have shown a correlation between the change in measuredSPV and a change in the fluid status of the patient. Typically, areduction in the fluid volume status of the patient results in anincrease in the measured SPV. While SPV is used in the presentdisclosure, it is to be understood that other dynamic pressure variablesmay be used in alternative embodiments. One non-limiting example ofanother dynamic pressure variable that may be used is that of pulsepressure variation.

FIG. 1 is a schematic diagram depicting an embodiment of a fluidassessment system 10. The fluid assessment system 10 includes a patientmonitor 12. The patient monitor 12 comprises one or more patientmonitors or other medical devices used to treat one or morephysiological conditions of the patient. The patient monitor 12 mayinclude, or be connected to, a blood pressure monitor 14 that monitorsthe patient blood pressure. In an embodiment, the blood pressure monitor14 may be an arterial blood pressure monitor, such as a catheter monitorthat is inserted into the patient's body and detects the blood pressureof the patient at any of a plurality of locations within the patient'scirculatory system. This embodiment produces a physiological signal thatis continuous in nature, such that the instantaneous arterial bloodpressure may be monitored. Alternatively, an intermittent signal may beproduced representative of the patient's instantaneous arterial bloodpressure at each cycle of the signal.

The patient monitor 12 further comprises or receives inputs from aventilator controller 16. The ventilator controller 16 controls theapplication of mechanical ventilation support to the patient. Thecontroller 16 provides the patient monitor 12 with signals indicative ofthe ventilation support provided to the patient. Alternatively, theventilation support provided to the patient may come from another sourcesuch as a hand bag and therefore the system 10 should not be limitedsolely to systems comprising a mechanical ventilator. Alternatively, thesignals indicative of the ventilation support provided to the patientmay come directly or indirectly from pressure and/or flow sensors (notdepicted) disposed within the breathing circuit (not depicted) connectedto the patient.

In one embodiment, the patient monitor 12 is connected to at least oneadditional medical device. The at least one additional medical devicemay be the blood pressure monitor 14 or the ventilator controller 16,but may be any other medical device for acquiring the physiological datafrom the patient. The at least one additional medical device may furtherbe a user input device (not depicted) which a clinician may use to enterpatient data.

The patient monitor 12 provides a measurement of the patient's SPV asobtained from the signal from the blood pressure monitor 14, to a fluidmodel 18. Alternatively, the patient's blood pressure may be provided tothe fluid model 18 wherein the SPV may be derived. The fluid model 18may be any type of fluid model as deemed suitable for the presentlydisclosed application as would be recognized by one skilled in the art.Exemplary embodiments of the fluid model 18 will be discussed in furtherdetail herein. In some embodiments, the fluid model 18 also receivesadditional patient specific information 22 from the patient monitor 12.The additional patient specific information 22 may include, in someembodiments, machine settings, such as an indication of the applicationof positive pressure ventilation; or other physiological parametersmeasured by the patient monitor 12, such as a measured current patientfluid status, respiration rate, or heart rate

In a default mode, the fluid model 20 may assume that the patient is ina normovolemic state. The fluid model 20 may also receive fluid statedata 24. The fluid state data 24 may indicate a patient fluid state thatis not normovolemic. In these instances, the fluid state data 24 (whichmay be a measurement of current patient fluid volume) would beincorporated into the fluid model 20 to more accurately reflect thepatient's current fluid state.

The fluid model 20 may also be connected to a physiological database 26.The physiological database 26 includes historical physiological data ofthe patient. Such a physiological database 26 may include a patient'selectronic medical record (EMR) or may include information relating toadditional physiological tests that have been performed on the patientrecently. The patient's EMR may include demographic information aboutthe patient and other medical history information. The physiologicaldatabase 26 provides to the fluid model 20 additional patient specificinformation 22 such as current patient medications, which may includeblood thinning or blood clotting agents; a physiological predispositionto a particular fluid status, such as hemophilia; patient demographicinformation; or patient medical history information that may help toindicate the patient's current fluid status and/or help to personalizethe fluid model.

The fluid model 20 receives some or all of the above-described inputsand uses those inputs to generate personalization constants 28 that areused in the fluid model 20 to tailor the application of the fluid model20 to the physiological condition of the specific patient. Apersonalized fluid model 30 is created using the fluid model 20 and thepersonalization constants 28. The personalization constants 28 may beconstant values or algorithms that more accurately describe thephysiology of the patient's circulatory system than the more generalfluid model 20. The personalization constants 28 may include moredetailed definitions of resistances, inductances, and compliances withinthe patient circulatory system. The personalized fluid model 30therefore provides a more accurate model representation of thecharacteristics of the patient's own circulatory system.

In an embodiment, the personalized fluid model 30 may be connected tothe patient monitor 12 through a personalization constant updater 32. Astime progresses, the physical characteristics of the patient'scardiovascular system may change. Changes to the resistance and/orcompliance of the patient's cardiovascular system may come about as adeterioration in the patient's health status, the introduction of newdrugs into the patient's system, the loss of fluid by the patient, ormany other physiological reasons for a change in cardiovascularproperties. The personalization constant updater 32 receives additionalpatient specific information 34 from the patient monitor 12 and usesthis additional patient specific information 34 to providepersonalization constant updates 36 to the personalized fluid model 30.The personalization constant updates 36 help to ensure that over time,the personalized fluid model 30 remains an accurate representation ofthe cardiovascular system of the patient.

Fluid status estimation begins when currently collected SPV data 18 istransferred from the patient monitor 12 to the fluid model 30. Transferof data can be automatic or initiated by a clinician. The personalizedfluid model then applies this newly acquired data to the personalizationconstants 28, or the personalization constant updates 36 and theequations of the personalized fluid model 30. The applications of theSPV data 18 to the personalized fluid model 30 results in an output of afluid status estimation 38. The fluid status estimation 38 may be madeand presented as either an estimation of patient blood volume or anestimation of relative change in blood volume. The fluid statusestimation 38 is visually presented to a clinician. The fluid statusestimation 38 may be presented on a graphical display, or may be printedout by a printer. The fluid status estimation 38 may be presented in atextual format to a clinician using e-mail or SMS messaging.

In one embodiment, the fluid status estimation 38 is made using a curvefitting or error limiting technique to “tune” the personalized fluidmodel 30 to match the contemporaneously monitored SPV 18. A fluid statusestimation component of the personalized fluid model 30 is adjusteduntil the SPV of the personalized fluid model 30 matches that of thecontemporaneously monitored SPV 18. The adjusted fluid status thatcoincides with the matching of the personalized fluid model SPV with thecontemporaneously monitored SPV 18 is determined to be the fluid statusestimation 38.

FIG. 2 is a schematic diagram of an embodiment of a fluid model 40 usedin conjunction with the fluid assessment system 10 as disclosed herein.The fluid model 40 is schematically represented as a circuit comprisinga plurality of circuit blocks connected in series and/or parallel torepresent the patient's cardiovascular system. The component blocks ofthe fluid model 40 include the right heart 42, which includes the rightatrium and right ventricle, the pulmonary vasculature 44, the lungs 46,the left heart 48, which includes the left atrium and the leftventricle, the aorta 50 the arterial vasculature 52, and the versusvasculature 54. Each of the component blocks comprises one or morecapacitors, inductors, or resistors that model the physiologicalproperties of each of the component blocks within the patient'scardiovascular system. Each component block also includes one or moreflow and/or pressure notations, each of these being indicative of theblood flow (f) and blood pressure (P) in the associated physiologicalcomponent within the patient.

As mentioned earlier, during PPV an additional pressure is applied tothe thoracic cavity of the patient. This results in changes to thehemodynamic properties within the patient's cardiovascular system. Inthe fluid model 40, the addition of PPV to the patient is represented bythe addition of voltage sources (P_(T)) to each of the patientphysiological components that are located within the thoracic cavity 56.Voltage waveforms representative of the cyclically changingintra-thoracic pressure can be applied to each of the voltage sourcesP_(T). These voltage waveforms can be modified to accurately reflect theintra-thoracic pressure generated based on the mechanical ventilationdelivered to the patient and/or patient physiological characteristicssuch as chest wall compliance.

As depicted in FIG. 2, the fluid model 40 is one example of the fluidmodel 20 used in the previously described fluid assessment system 10. Asstated above, by solving for one or more of the variables in fluid model40 and replacing them with personalization constants, the fluid model 40can be personalized to more accurately reflect the physiologicalproperties of that specific patient. Thus, the fluid model 40 can bemodified to create the personalized fluid model 30.

As described above with respect to FIG. 1, the personalization constantupdater 32 provides updated personalization constants 36 to thepersonalized fluid model 30. While this may incorporate updates ofphysiological data such as would result in the modification of one ormore of the personalization constants, another type of update may be aphysiological change that must be added to the personalized fluid model.Such physiological change may include that of a patient bleeding whichmay be represented by the simulated bleeding component 58. The simulatedbleeding component 58 is modeled with the proper resistance (Rb) andflow (F_(b)) values such as to model a patient that is actively losingblood at a known rate (F_(b)). Such an addition to the fluid model 40further helps to more accurately represent the current fluid status ofthe patient.

Similarly, a simulated infusion component 60 can be added to the fluidmodel 40 such as to represent the known infusion of fluid into thepatient's cardiovascular system at a known flow rate. Thus, simulatedinfusion component may include a resistance (R_(t)) at a known flow(f_(t)) as with the simulated bleeding component 58, the addition of asimulated infusion component 60 may help to provide a more accuratereflection, and resulting estimation, of the patient's current fluidstatus.

In order to correlate the fluid model 40 to the measured SPV from thepatient, the proper location and physiological component for the SPVmeasurement must be located within the fluid model 40. Often, arterialblood pressure is taken via a catheter from the patient's aorta. Assuch, for exemplary purposes, this pressure location coincides withreference point 62 located within the aorta component 50 of the fluidmodel 40.

Thus, the pressure at reference point 62 may be used in two ways inconjunction with the fluid model 40. First, the fluid model 40 may beused in a predictive fashion in order to estimate the continuous bloodpressure and thus the SPV measured at the aorta for a patient whoexperiences a specific amount of blood loss. Alternatively, thepatient's measured continuous blood pressure may replace the variablevalue of the pressure at reference point 62, and the model can be usedto estimate blood loss or personalized constants.

If the patient's fluid loss is unknown, then the fluid model 40 is tunedin order to determine a value for the reduced volume of blood in thecardiovascular system or may be tuned to identify the flow rate of bloodloss in the simulated bleeding component 58.

While the fluid model 40 has been used in an exemplary fashion, thefluid models as used in the herein disclosed system and method are notso limited to the specific fluid model 40 disclosed. The fluid modelused may be significantly more or less complex than the exemplary fluidmodel 40. Any of the fluid models as would be recognized by one skilledin the art could be suitable in embodiments depending upon thespecificity desired by the model and the available known inputs that maybe added to the model in order to personalize the model for the patient.

FIG. 3 is a flow chart depicting the steps of an embodiment of a methodof providing a personalized fluid assessment 100.

First, at step 102 a fluid model is obtained. The fluid model may belocally stored on a device that may be used in conjunction with thedisclosed method. Alternatively, the fluid model may be stored at aremote location such that the fluid model must be obtained in step 102via a communications platform such as the Internet, telecommunications,or an IT network. In a still further embodiment, the fluid model can bephysically entered or defined by the clinician at the start ofperforming the method 100.

Next, patient blood pressure data is acquired in step 104. Typically,this blood pressure data is continuous blood pressure data, as may beobtained through an arterial catheter. Alternatively, the blood pressuredata is acquired intermittently, but at regular intervals at arelatively frequent rate (i.e., 0.1 Hz or greater). In an exemplaryembodiment, the acquired blood pressure data is continuous bloodpressure data spanning at least one breath cycle. The blood pressuredata acquired in step 104 may further include a determination of thepatient SPI as obtained from the acquired blood pressure data.

The blood pressure data acquired in step 104 is then applied to thefluid model in step 106. In alternative embodiments, first additionalpatient information parameter is obtained beyond the patient bloodpressure data acquired in step 104. This additional patient informationis acquired in step 110. The obtained first physiological data in step110 may include an identification of whether or not the patient isreceiving positive pressure ventilation, an indication of the airwaypressure that is delivered to the patient, the patient's demographicinformation, medical history, other monitored physiological parameters,or machine settings. Alternative types of first additional patientinformation that may be acquired at step 110 may include a measure ofthe patient's chest wall compliance, information regarding current drugsthe patient is receiving, or other information regarding patientpreexisting conditions. The first additional patient information may beobtained by the same patient monitor device that acquires the patientblood pressure data, or may be obtained from another device or enteredmanually by a clinician.

In step 106, all of the data acquired in step 104 and optionally in step110 are applied to the fluid model obtained in step 102. By applying theacquired data to the fluid model, particular values in the fluid modelare defined such as to represent the current fluid status andphysiological condition of the patient. These defined values arereferred to as personalization constants. The end result of theapplication of the acquired data to the fluid model in step 106 is tocreate a personalized fluid model in step 112. The personalized fluidmodel created in step 112 includes the personalization constants thathave been derived to more accurately reflect the status andphysiological condition of the patient based upon the data acquired instep 104 and/or step 110.

Next, in optional steps, second additional patient information may beobtained in step 114. This second additional patient information may beacquired at a later time or date, especially at a time or data proximalto when the personalized fluid assessment is desired. The secondadditional patient information obtained in step 114 is then used in step116 to update the personalized fluid model created in step 112. Thisprovides an advantage in that the personalized fluid model created instep 112 is updated in step 116 to account for changes in the patientfluid status or physiological condition that have occurred since thepersonalized fluid model was created in step 112. The inclusion of thesechanges in fluid status or physiological condition may help to improvethe accuracy of the personalized fluid assessment produced inembodiments of the method disclosed herein.

Next, regardless of whether the personalized fluid model created in step112 or the updated personalized fluid model from step 116 is used, instep 118 new patient blood pressure data is acquired. The new patientblood pressure data most accurately reflects the physiological status ofthe patient at the time when the personalized fluid assessment isdesired. The newly acquired blood pressure data may also include adetermination of the blood pressure SPV as well.

Next, in step 120, the newly acquired blood pressure data is applied tothe personalized fluid model from either step 112, or optionally step116. By the introduction of the newly acquired blood pressure data intothe personalized fluid model, the fluid model may be used to derive anestimate of the patient's current blood volume, and or blood volumechange, based upon the measured blood pressure and the SPV. Thus, instep 122, a patient fluid status estimate is produced.

The new blood pressure data is applied to the personalized fluid modelin step 120 by comparing a derived value of the blood pressure SPV fromthe personalized fluid model to the SPV of the newly acquired bloodpressure data. The personalized fluid model is then modified to adjustthe patient fluid volume status in order to match the derived SPV withthe currently measured SPV using a curve fitting or error limitingtechnique. One such curve fitting or error limiting technique that maybe used in the comparison of the derived and the measured SPV values isthat of a minimum square error technique. The fluid status of thepersonalized fluid model is adjusted until the derived SPV and the newlyacquired SPV match. The fluid status used in the personalized fluidmodel when a match is achieved is the estimated fluid status for thepatient produced in step 122.

Some embodiments of the system and method as disclosed herein may beimplemented solely through the use of a computer. Such embodiments maybe implemented through the use of computer readable code stored on acomputer readable medium. Such computer readable code may definemodules, or sub-programs that perform the step of an embodiment of themethod as disclosed herein. In such computer implemented embodiments,the technical effect of the system and method as disclosed herein may bethat of providing a personalized fluid assessment based upon one or morereadily obtainable patient physiological parameters.

Embodiments of the system and method as presented disclosed may furtherprovide the advantage of providing a single fluid status indicator thatmay be used to normalize patient fluid status monitoring techniques.Such embodiments may provide the advantage of providing an indication offluid status in a less invasive manner then some previously implementedtechniques. Embodiments as disclosed herein may also present theadvantage of providing fast and accurate assessment of a patient's fluidstatus that is not labor intensive on the part of the clinician.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent elements with insubstantial differences form the literallanguages of the claims.

Various alternatives and embodiments are contemplated as being with inthe scope of the following claims, particularly pointing out anddistinctly claiming the subject matter of the present disclosure.

1-12. (canceled)
 13. A fluid status estimation system, the systemcomprising: a patient monitor connected to a patient to receive firstblood pressure data and second blood pressure data; a first fluid modelthat receives the first blood pressure data from the patient monitor anduses the first blood pressure to derive at least one personalizationconstant; and a personalized fluid model comprising the at least onepersonalization constant that receives the second blood pressure datafrom the patient monitor, and uses the second blood pressure data toproduce an estimate of patient fluid status.
 14. The fluid statusestimation system of claim 13 wherein the first and second bloodpressure data comprises dynamic blood pressure data.
 15. The fluidstatus estimation system of claim 14 wherein the first fluid modelfurther receives first additional patient information, the personalizedfluid model being further derived from the application of the firstadditional patient information to the first fluid model.
 16. The fluidstatus estimation system of claim 15 further comprising apersonalization constant updater, the personalization constant updaterreceiving second additional patient information and deriving at leastone personalization constant update, the at least one personalizationconstant update being applied to the personalized fluid model.
 17. Asystem for estimating the fluid status of a patient, the systemcomprising: a patient monitor connected to the patient and at least oneadditional medical device, the patient monitor receiving first bloodpressure data and updated blood pressure data from the patient andreceiving first additional patient information and second additionalpatent information from the at least one additional medical device; afirst fluid model that receives the first blood pressure data and firstadditional patient information from the patient monitor, the first fluidmodel being used with the first blood pressure data and the firstadditional patient information to derive at least one personalizationconstant; a personalization constant updater that receives the secondadditional patient information from the patient monitor and calculatesan updated value of the at least one personalization constant; and apersonalized fluid model comprising the at least one personalizationconstant, the personalized fluid model receiving the updated value andreplacing the at least one personalization constant with the updatedvalue.
 18. The system of claim 17 wherein the patient monitor receivessecond blood pressure data from the patient and transmits the secondblood pressure data to the personalized fluid model, the second bloodpressure data being applied to the personalized fluid model to derive anestimation of the fluid status of the patient.
 19. The system of claim18 further comprising a physiological database comprising additionalpatient specific information, and wherein the first fluid model receivesthe additional patient specific information from the physiologicaldatabase, and the at least one personalization constant being furtherderived from the application of the additional patient specificinformation to the first fluid model.
 20. The system of claim 18 furthercomprising a graphical display that receives the estimation of the fluidstatus of the patient and visually presents the estimation of the fluidstatus of the patient.
 21. The system of claim 20, wherein apharmacokinetic or a pharmacodynamics model is adjusted based upon thepresented estimation of the fluid status of the patient.
 22. The systemof claim 20, wherein a provision of anesthetic agent is adjusted basedupon the presented estimation of the fluid status of the patient. 23.The system of claim 18, further comprising a catheter monitor configuredto be inserted into the patient, the catheter monitor beingcommunicatively connected to the patient monitor to provide continuousmeasurements of blood pressure data.
 24. The system of claim 23, whereinthe first and second blood pressure data are systolic pressurevariations.
 25. The system of claim 23, wherein the first and secondblood pressure data are pulse pressure variations.
 26. The system ofclaim 17, wherein at least one additional medical device comprises amechanical ventilator and the first and second additional patientinformation is indicative of the mechanical ventilation provided to thepatient.
 27. The system of claim 26, wherein the first and secondadditional patient information is indicative of the application ofpositive pressure ventilation to the patient by the mechanicalventilator.
 28. The system of claim 13, further comprising a graphicaldisplay that receives the estimation of the fluid status of the patientand visually presents the estimation of the fluid status of the patient,and wherein a provision of anesthetic agent is adjusted based upon thepresented estimation of the fluid status of the patient.
 29. The systemof claim 13, wherein a provision of anesthetic agent is adjusted basedupon the produced estimate of patient fluid status.
 30. The system ofclaim 13, further comprising a catheter monitor configured to beinserted into the patient, the catheter monitor being communicativelyconnected to the patient monitor to provide continuous measurements ofblood pressure data.
 31. The system of claim 30, wherein the first andsecond blood pressure data are dynamic pressure variables.
 32. Thesystem of claim 31, wherein an error limiting technique is applied tothe personalized fluid model using the at least one personalizationconstant until a calculated blood pressure value matches the secondblood pressure data, and a resulting fluid status estimation is theestimate of patient fluid status.